Multi-zone carrier head for chemical mechanical polishing and cmp method thereof

ABSTRACT

A multi-zone carrier head includes a housing; a retaining ring secured to a lower edge of the housing; a backing plate having a plurality of non-concentric pressure zones defined by a plurality of isolated apertures on the backing plate; wherein the backing plate has a wafer side and a non-wafer side, the wafer side facing a backside of a wafer during a CMP operation; and a plurality of pneumatic bladder for independently controlling pressure exerted in the respective non-concentric pressure zones on the backside of the wafer during the CMP operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to chemical mechanical polishingof substrates and, more particularly, to a multi-zone carrier head forchemical mechanical polishing.

2. Description of the Prior Art

In the process of fabricating integrated circuits, it is essential toform multi-level material layers and structures on a wafer. However, theprior formations often leave the top surface topography of an in-processwafer highly irregular. Such irregularities cause problems when formingthe next layer over a previously formed integrated circuit structure.For example, when printing a photolithographic pattern having smallgeometries over previously formed layers, a very shallow depth of focusis required. Therefore, there is a need to periodically planarize thewafer surface.

One technique for planarizing the surface of a wafer is chemicalmechanical polishing (CMP). In CMP processing, a wafer is placed facedown on a rotating platen. The wafer, held in place by a carrier orpolishing head, independently rotates about its own axis on the platen.Typically, the head is a floating polishing head with a flexiblemembrane. On the surface of the platen is a polishing pad over whichthere is dispensed a layer of polishing slurry. The slurry chemistry isessential to proper polishing. Typically, it consists of a colloidalsolution of silica particles in a carrier solution.

Conventional CMP suffers from some problems that need to be accountedfor during the process integration. When polishing a wafer that has stepfeatures, only the top of the features touch the polishing pad,concentrating the pressure on these contact points. This increases thepolishing rate above that of a blanket wafer. In addition, it causesnon-uniformity in the removal rate across patterns of differentdensities due to variations in the pressure distribution across thepattern. This pattern density effect on removal rate can cause problemsif there are both dense pattern and very sparse pattern on the wafersurface.

SUMMARY OF THE INVENTION

In one aspect, the invention is directed to a multi-zone carrier headfor chemical mechanical polishing (CMP). The multi-zone carrier headincludes a housing; a retaining ring secured to a lower edge of thehousing; a backing plate having a plurality of non-concentric pressurezones defined by a plurality of isolated apertures on the backing plate;wherein the backing plate has a wafer side and a non-wafer side, thewafer side facing a backside of a wafer during a CMP operation; and aplurality of pneumatic bladder for independently controlling pressureexerted in the respective non-concentric pressure zones on the backsideof the wafer during the CMP operation.

In another aspect, the invention is directed to a method for polishing asubstrate or wafer. The method includes the following steps:

(a) mounting a substrate into a carrier head, the carrier headcomprising a pneumatic means controlled by a control unit forindependently controlling pressure exerted in respective non-concentricpressure zones on backside of the substrate;

(b) rotating the carrier head and a polishing pad on which the substrateis resting;

(c) providing a down force on the substrate; and

(d) polishing a material layer of the substrate away.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompany drawings are included to provide a further understandingof the invention, and are incorporated in and constitute a part of thisspecification. The drawings illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a diagram showing a table based CMP tool;

FIG. 2 is a schematic, cross-sectional diagram illustrating thestructure of a carrier head in accordance with one preferred embodimentof this invention;

FIG. 3 illustrates a plane view of the backing plate according to onepreferred embodiment;

FIG. 4 illustrates a plane view of the backing plate according toanother preferred embodiment; and

FIG. 5 is a schematic, cross-sectional diagram illustrating thestructure of a carrier head in accordance with another preferredembodiment of this invention.

DETAILED DESCRIPTION

FIG. 1 is a diagram showing a table based CMP tool 50. The table basedCMP tool 50 includes a carrier head 52, which holds a wafer 54, and isattached to a translation arm. In addition, the table based CMP tool 50includes a polishing pad 56 that is disposed above a polishing table 58,which is often referred to as a polishing platen.

In operation, the carrier head 52 applies downward force to the wafer54, which contacts the polishing pad 56. Reactive force is provided bythe polishing table 58, which resists the downward force applied by thecarrier head 52. A polishing pad 56 is used in conjunction with slurryto polish the wafer 54. Typically, the polishing pad 56 comprises foamedpolyurethane or a sheet of polyurethane having a grooved surface. Thepolishing pad 56 is wetted with polishing slurry having both an abrasiveand other polishing chemicals. In addition, the polishing table 58 isrotated about its central axis 60, and the carrier head 52 is rotatedabout its central axis 62.

FIG. 2 is a schematic, cross-sectional diagram illustrating thestructure of a carrier head in accordance with one preferred embodimentof this invention. As shown in FIG. 2, the carrier head 52 generallyincludes a housing 150, a retaining ring 152, a disk-shaped backingplate 154 and a backing film 156.

The housing 150 can be connected to a drive shaft (not shown) to rotatetherewith during polishing about an axis of rotation 62, which issubstantially perpendicular to the surface of a polishing pad 56. Thehousing 150 may be generally circular in shape to correspond to thecircular configuration of the wafer to be polished. Passages (not shown)may extend through the housing 150 for pneumatic control of the carrierhead 52. O-ring may be used to form airtight seals between the passagesthrough the housing 150 and passages through the drive shaft.

The wafer 54 is held in place on the carrier head 52 by the retainingring 152. The retaining ring 152 may be a generally annular ring securedalong a lower, outer edge of the housing 150. The retaining ring 110defines a pocket area for accommodating the wafer 54. An inner surfaceof the retaining ring 152 engages the wafer 54 to prevent it fromescaping from beneath the carrier head 52.

The backing film 156 is attached to the backing plate 154 between thebacking plate 154 and the wafer 54. The backing film 156 cushions thewafer 54 during the polishing and compensates for slight flatnessvariations in the wafer 54 or backing plate 154. The backing film 156may be made of polymer materials and attached to the backing plate 154with a pressure sensitive adhesive, but not limited thereto.

In addition, the carrier head 52 may includes a diaphragm seal 158 thatis generally an annular ring of a flexible material. An outer edge ofthe diaphragm seal 158 is clamped between the housing 150 and theretaining ring 152, and the inner edge of the diaphragm seal 158 issecured to the backing plate 154 by, for example, a clamp ring (notshown). The diaphragm seal 158 may be formed of rubber, such asneoprene, an elastomeric-coated fabric, such as NYLON™ or NOMEX™,plastic, or a composite material, such as fiberglass.

The backing plate 154 may be a flat stainless steel disk slightly largerthan the wafer 54. The backing plate 154 presses against the backside ofthe wafer 54 and transfers the polishing force to the wafer during a CMPoperation.

The backing plate 154 has a plurality of non-concentric pressure zonesdefined by an isolated central aperture 162 that is formed in a centrallocation of the backing plate 154 and a plurality of isolated peripheralapertures 164 surrounding the central aperture 162.

The backing plate 154 has a wafer side and a non-wafer side, the waferside facing a backside of the wafer 54 during a CMP operation.Preferably, the number of the non-concentric pressure zones is equal toor larger than five.

FIG. 3 illustrates a plane view of the backing plate 154 according toone preferred embodiment. FIG. 4 illustrates a plane view of the backingplate 154 according to another preferred embodiment. In FIG. 3, thereare six non-concentric pressure zones distributed on the backing plate154, wherein the central aperture 162 is surrounded by the peripheralapertures 164. The central aperture 162 is circular, while theperipheral apertures 164 are sector shaped.

In FIG. 4, there are nine non-concentric pressure zones distributed onthe backing plate 154, wherein the central aperture 162 is square orrectangular. However, it is understood that the number of thenon-concentric pressure zones provided by the backing plate may exceednine and the arrangement and distribution of the non-concentric pressurezones depicted in FIGS. 3 and 4 are exemplary.

Referring back to FIG. 2, the carrier head 52 further comprises aplurality of pneumatic bladders 182 and 184 that are provided withincorresponding central aperture 162 and peripheral apertures 164 forindependently controlling the down force within each of thenon-concentric pressure zones on the back side of the wafer 54. Theinflation or deflation is accomplished by using the respective passagesthat connects with air supply or pumps.

According to another preferred embodiment of this invention, referringto FIG. 5, the carrier head 52 further comprises pressure-sensingelements 192 and 194 provided in respective non-concentric pressurezones. The pressure-sensing element 192 is installed in the centralaperture 162, while the pressure-sensing elements 194 are installed inrespective peripheral apertures 164.

The pressure-sensing elements 192 and 194 may be piezo-materials,piezo-crystals, piezo sensors or piezoelectric ceramic sensors. Forexample, the pressure-sensing elements 192 and 194 may comprise BaTiO₃,AIN, ZnO, lead zirconium titanate (PbZrTi) or PZT ceramic, tantalumoxide (Ta₂O₅), barium strontium tantanite (BST) or the like.

It is one salient feature of the present invention that thepressure-sensing elements 192 and 194 can detect the topography of thewafer surface during a CMP operation and transmit feedback signals to acontrol unit of the CMP tool. According to the feedback signals, thecontrol unit, for example, a computer, which is capable of controllingthe air supply or pumps, can alter, in real time, the pressure exertedin each non-concentric pressure zones by means of the pneumatic bladders182 and 184, thereby improving uniformity and better planarization.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A multi-zone carrier head for chemical mechanical polishing (CMP),comprising: a housing; a retaining ring secured to a lower edge of thehousing; a backing plate having a plurality of non-concentric pressurezones defined by a plurality of isolated apertures on the backing plate;wherein the backing plate has a wafer side and a non-wafer side, thewafer side facing a backside of a wafer during a CMP operation; apneumatic means for independently controlling pressure exerted in therespective non-concentric pressure zones on the backside of the waferduring the CMP operation; and a pressure-sensing element disposed underthe pneumatic means in the respective non-concentric pressure zones. 2.The multi-zone carrier head for CMP according to claim 1, furthercomprising a backing film attached to the wafer side of the backingplate, wherein the backing film is disposed between the backing plateand the backside of the wafer during the CMP operation.
 3. Themulti-zone carrier head for CMP according to claim 1, wherein pluralityof isolated apertures on the backing plate include a central apertureand peripheral apertures surrounding the central aperture.
 4. Themulti-zone carrier head for CMP according to claim 1, wherein themulti-zone carrier head further comprises a diaphragm seal.
 5. Themulti-zone carrier head for CMP according to claim 4, wherein thediaphragm seal is an annular ring of a flexible material.
 6. (canceled)7. The multi-zone carrier head for CMP according to claim 1, wherein thepressure-sensing element includes piezo-materials, piezo-crystals, piezosensors or piezoelectric ceramic sensors.
 8. The multi-zone carrier headfor CMP according to claim 1, wherein the pressure-sensing element isselected from the group consisting of BaTiO3, AIN, ZnO, lead zirconiumtitanate, PZT ceramic (PbZrTi), tantalum oxide (Ta205), and bariumstrontium tantanite (BST).
 9. The multi-zone carrier head for CMPaccording to claim 1, wherein the pressure-sensing element detectstopography of the wafer during the CMP operation and transmits feedbacksignals to a control unit.
 10. A method for polishing a substrate,comprising: mounting a substrate into a carrier head, the carrier headcomprising a pneumatic means controlled by a control unit forindependently controlling pressure exerted in respective non-concentricpressure zones on backside of the substrate and a pressure-sensingelement under the pneumatic means in the respective non-concentricpressure zones; respectively rotating the carrier head and a polishingpad on which the substrate is resting; providing a down force on thesubstrate; and polishing a material layer of the substrate away. 11.(canceled)
 12. The method of claim 10, wherein the pressure-sensingelement includes piezo-materials, piezo-crystals, piezo sensors orpiezoelectric ceramic sensors.
 13. The method of claim 10, wherein thepressure-sensing element is selected from the group consisting ofBaTiO3, AIN, ZnO, lead zirconium titanate, PZT ceramic (PbZrTi),tantalum oxide (Ta205), and barium strontium tantanite (BST).
 14. Themethod of claim 10, wherein the pressure-sensing element detectstopography of the substrate during a CMP operation and transmitsfeedback signals to a control unit.